Let and expr shell operations compare let's win

Integer operations in shell scripts are generally implemented by the two instructions of let and expr, such as the variable s plus 1 can be written: let "s = $s + 1" or s= ' expr $s + 1 '
The two are not easy to write, but the performance of the comparison can be an example to show you:

1. Expr script and execution time:

　　

#!/bin/bashs=0while [$s-lt 10000]do       s= ' expr $s + 1 '       echo $s >>/dev/null 2>&1done[[email protected] ~]# time sh expr.sh real    0m50.776suser    0m11.528ssys     0m39.601s

2. Let script and execution time:

#!/bin/bashs=0while [$s-lt 10000]do let       "s = $s + 1"       echo $s >>/dev/null 2>&1done[[email protected ] ~]# time sh let.sh real    0m0.875suser    0m0.676ssys     0m0.199s

With the above two examples, it goes without saying that it is clear that let's win with super-high advantage, so get expr dozens of times times!

Transferred from: http://yooma.blog.51cto.com/6965726/1187063/

Let and expr shell operations compare let's win